Can I put a line break between "von" and "Neumann"?

My answer would be to allow considerations of language and sense to outweigh those of layout and appearance. Thus 'John von Neumann' should all be on the same line.

Setting type has changed drastically from the days of metal and phototypesetting. The responsibility for composing type no longer lies with a highly skilled, dedicated typographer, but more often with a designer or production artist, who may not be trained in this skill.

'Breaking for sense' means not letting the software make automatic breaks, but evaluating the text, and making considered line breaks when necessary.

When breaking for sense, strive to:

Keep important phrases together
Avoid hyphenations
Break a line after punctuation
Pair adjectives with their nouns
Keep proper names together
Avoid widows
Group color and typestyles together

Fine Typography: breaking for sense

Further considerations:

Do not break up linguistic units among lines.

[..]

When absolutely necessary to keep linguistic units together (like a person’s name), then the line break should still not cause a line to be more than 50% shorter than the other line.

English line breaking rules

How to break lines

In general, if there's a whitespace, there's reasonable grounds to consider the letters on each side to constitute separate morphemes and thus allow splitting.

Anything else is a subjective matter of type-setting and layouting.